The Physiology of Fitness

Responses to acute exercise

Musculoskeletal Responses

The musculoskeletal system consists of muscles, bones, joints, tendons and ligaments; it is the muscular and skeletal system combined. Before you exercise, you need to warm up as this prepares the body for different movement in activities and it reduces the risk of injury. Then you carry out mobilisation activities which increase the joint mobility; it enables the joints to become more lubricated by releasing more synovial fluid onto them.

Increased blood supply

There is a continuous circulation of blood in the body. It transports oxygen, carbon dioxide, nutrients, hormones and metabolic waste around the body. During exercise, when your body works 'overtime' your heart rate increases so more blood is needed within the muscles. When our heart rate increases it enables oxygen-rich blood to be pumped around the body at a faster rate which warms our muscles and helps to deliver more oxygen to the working muscles. There is a bigger demand for oxygen because the muscles are working more than usual so they need more energy. The blood from other body parts such as organs is reduced. This is known as 'redistribution'. The blood vessels in your muscles dilate and the blood flows around the body at a faster rate because of the bigger oxygen demand. The ATP gets used up in the working muscle producing several metabolic byproducts such as adenosine, hydrogen ions and CO2 which leaves and causes capillaries in the muscle to dilate (expand). This increase in blood supply allows for more waste products to be carried away from the working muscles, therefore it helps to reduce the build up of lactic acid.

Increase in muscle pliability

The muscle spindles that are located within muscle fibres stretch when nerve impulses are made and the information for the degree of the stretch is sent to the nervous system. As the tissues warm up, the rate of nervous impulses also increase and so does the speed of the nervous transmission.

When you exercise, more blood is pumped through the muscles as excess heat is generated so the muscle tissue warms up. The muscles become more pliable which means they are able to change shape more easily. So, they can adjust and are flexible. The msucles adjust so that the lactic acid present in the muscles clears up; by doing this they can become more pliable to different movements. This allows you to stretch to greater lengths without tearing muscles and decreases the risk of getting muscle strains. For example, Plasticine pulls apart when it is cold and stretches when it's warm just like muscles.

I recorded my flexibility with the sit and reach test before exercise and I got 30cm. Then during exercise I got 30cm, then I got 31cm after exercise. This shows that the muscles became more pliable once they had warned up after exercise.

Increased range of movement

The bones in the body are help together by joints which allow movement between them. The degree of the joint movement is known as the range of motion. Doing exercise means our joints are moving quickly so there needs to be more synovial fluid in the joints to allow this movement. The joints become warmer as exercise increases the body temperature and the synovial fluid becomes thinner, making the movement more efficient. To achieve a full range of movement you need to start doing small movements and gradually get larger until a full range of movement is reached. If you have increased muscle pliability then it will allow for a wider range of movement and reduce the risk of any injuries. The range of movement and mobility of the joints increases due to the synovial fluid being thinner and warmer, which causes an increased elasticity of tendons and ligaments. The joints that need to be mobilised are: Shoulders, elbows, spine, hips, knees and ankles.

Muscle fibre micro tears

Every muscle in the body is made up of thousands of fibres which pull against each other. There are microfilaments (actin, myosin) found in muscle cells that enable it to contract. Depending on the intensity and duration of the exercise you are doing, you could feel aching in your muscles. There are more fibres that are involved in contracitons when you exercise so they are stronger and it meand that you have less opportunity to rest. During resistance exercise, the muscle fibre 'breaks' which are called micro-tears or micro-trauma as the damage is minimal. This happens when muscles are put under excessive stress such as lifting weights. The myosin heads and the actin filaments are pulled from the myofibrils as the muscles are liftings weights that they can't hold. The damage causes a release of chemicals that cause mild to moderate soreness and stiffness. If it lasts a few hours or hurts the day after, it is referred to as DOMS which is delayed onset muscle soreness. Other pains resulting from intense exercise are aching, fatigue and a limited range of movement. During rest from training/exercise, if any damage has occured then the muscle will react by adding proteins and the chemicals stimulate growth and repair in the area. So, it rebuilds becoming bigger and stronger over time. This process is called muscle hypertrophy.

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Energy System Responses

There are three energy systems: Phosphocreatine, lactic acid and aerobic system. In order to make the muscle fibres contract, energy is required. All three energy systems contribute at the start of exercise but the method by which the body produces the energy is determined by the intensity and duration of the activity being undertaken.

Phosphocreatine System

This system is anaerobic and made up of a phosphate and creatine molecules (PC). It supplies the majority of ATP and a much quicker rate as it is the immediate energy system. During this process, ATP breaks down into ADP + P + energy. So, 1 phosphocreatine molecule is produced with no waste products. It is efficient as less energy is required to resynthesise ATP than is needed to break it down. the resynthesis equation is energy + ADP + P= ATP. The PC stores are used for rapid, high-intensity contractions (95-100% maximum) when explosive work can be achieved like sprinting 100m and jumping. There is a high energy compound between the bonds so that when it breaks down, large amounts of energy are released. However, it can only be used for short periods at around 10 seconds as the supply is very limited. The system hasa a quick recovery and it can be used again after 30 seconds to 4 minutes.

Lactic acid System

When the PC stores run out, this system is then used which is also anaerobic. It is also known as the 'anaerobic glycolysis' system and is a short-term energy system used to meet energy requirements for higher intensity over a long period of time, such as during a 400m race. It is produced quickly but not as fast as the PC energy system; it usually lasts around 60 to 90 seconds of maximal work. The ATP is produced from the breakdown of glucose to pyruvate in the muscle cells but because there is no oxygen present, lactic acid is produced and ATP forms. The limiting factor is the present lactic acid as it acts as a poison to the muscles causing fatigue and soreness. This system has a longer recovery time before it can be used again; it takes around 2 minutes to 2 hours to break down the lactic acid.

Aerobic System

This system requires oxygen and produces ATP at a slower rate when you are at rest or doing low-intensity exercise like a marathon or long distance cycling or swimming. So it is a long-term energy system and if plenty of oxygen is available as it is during everyday movements and light exercise, glycogen and fatty acids break down to produce large amounts of ATP. The oxygen available is used to break down glucose to pyruvate but because oxygen is present, it can't turn to lactic acid so it goes through chemical reactions like Krebs Cycle and Electron transport chain to break down molecules as it can't turn straight to lactic acid. There are no waste products like lactic acid and it produces water and heat and releases carbon dioxide. It uses a series of reactions, one being aerobic glycolysis. It takes place in organelles called mitochondria which is important for energy production. This system has a slow recovery as it takes the amoun t of time to eat (carbohydrates which give you more energy) and drink to be able to replenish the stores.
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The Energy Continuum

The energy continuum is the term used to describe the types of energy systems used during physical activities. The energy systems all work together and what we do determines which energy system supplies the majority of ATP. The energy continuum highlights which system produces the most amount of energy at different stages of an activity. More ATP is needed when we do exercise so we use the phosphocreatine system for short bursts of energy like during a 100m sprint and the lactic acid system when the PC stores run out. But when we rest, all of our energy is supplied by the aerobic system. We also use this system during long periods of exercise like a marathon. Some sports need all three energy systems, for example, football because the intensity varies from low to very high. Our body uses the food we have eaten, converted by energy systems to produce energy. Different sports have different energy requirements.

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Cardiovascular Responses

Consists of the heart and blood vessels through which the heart pumps blood around the body. During exercise, the system changes to ensure that muscles receive the required amount of O2 and nutrients. The resting heart rate decreases in trained individuals due to the more efficient circulatory system.

Heart rate anticipatory Response

Before exercise even begins, heart rate increases in anticipation. It is started through the release of neurotransmitters called epinephrine and norepinephrine (known as adrenaline and noradrenaline). Adrenaline is a hormone released during times of stress which gets the body ready for action. They cause your heart to beat faster.

I recorded my heart rate before exercise and it was 65 beats per minute, then during exercise it was 127 beats per minute and after exercise it was 90 beats per minute. This shows that it increased due to the exercise but afterwards it slowly started to decrease.

Activity Response

As you start exercise, your heart rate increases which is equal to the increase in intensity until you are near exhaustion. As you approach this point your heart rate levels off, this is your heart rate maximum. When we start exercising, our heart rate increases which allows for a continuous production of energy for contractions as we need more oxygen to be delivered to working muscles. When the muscle action increases, the heart beats at a quicker rate to send more oxygen to the cells. This is because a great volume of blood is released with each stroke.

Increased blood pressure

When we exercise, our blood pressure increases which is needed for the blood to flow around the body quicker. The contraction of the heart produces this blood pressure as it pushes blood into the blood vessels. The heart contracts faster as the heart rate increases which leads to an increased blood pressure. When your blood pressure is taken, two values are given: Systolic (when the heart is contracting) and Diastolic (when the heart is relaxing). When you rest, a healthy individual should have a blood pressure ranging from 110-140mmHg for systolic and 60-90mmHg for diastolic. During exercise, the systolic should increase to 200mmHg- 250mmHg for healthy exercise and the diastolic shouldn't hardly change even if you are exercising. It can decrease because of the dilated blood vessels in the working muscles that let heat escape. If it increases by 15mmHg it could indicate that you have coronary heart disease.

Vasoconstriction and Vasodilation

Vasoconstriction is the narrowing of blood vessels by small muscles in their walls so the blood flow is restricted/slowed. Blood flows through arteries, arterioles, capillaries, veins and venules and it is directed where it is needed. For example, while eating it would be at your stomach and for running it would be aimed at your leg muscles. So less blood is pumped to organs that don't need oxygen. During exercise, blood flows through blood vessels near the skin's surface to help cool the body down. Vasodilation is where the blood vessels close to the skin surface enlarge. When you exercise, your face goes red as your body temperature rises; this is because the heat disperses when the blood vessels expand.
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Respiratory Responses

The Respiratory System consists of the lungs, gas exchange and other organs involved in breathing. The function of it is to provide a continuous and adequate supply of oxygen to the tissues, enable the removal of CO2 from the body, to assist in the upkeep of the pH of the body and to assist in the control of body temperature.

Increase in breathing rate

The number of breaths per minute increases due to neural and chemical influences. The rate and depth of breathing is controlled by the respiratory centre located in the Medulla (brain stem) which sends neural impulses to the respiratory muscles. Also, chemoreceptors are located around the body but mainly in the bigger blood vessels like the aorta. These are sensitive to chemicals such as O2, CO2 and pH levels within the blood. If they detect a change in normal levels, they stimulate the body to remove them by increased breathing.

Pulmonary ventilation is the amount of air we breathe in and out per minute (VE). It is worked out by the frequency x tidal volume (Breaths per minute x volume of air in one breath). The average breathing rate is 12 per minute, the average tidal volume is 0.5 and the average VE is 12 x 0.5 =6 litres.

I recorded by breathing rate before exercise which was 18 per minute, then during exercise it was 38 but then it dropped to 22 after exercise. This shows an increase in the breathing rate when exercising but it starts to lower when you start to exercise.

Intercostal muscles

The intercostal muscles are thin bands of muscles which function to move and stabilise the chest wall and are located between the ribs. There are two kinds: internal and external which help with inspiration and expiration during exercise. The external intercostal muscles contract and elevate the ribs during inspiration and expand the chest cavity. The internal intercostal muscles are responsible for forced exhalation; they lower the ribs and decrease the space in the chest cavity. During strenuous exercise, the abdominal muscles help to aid expiration.
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Increased tidal volume

Tidal volume is the volume of air moved between one normal inhalation and one normal exhalation. So, there is no extra effort is made to increase are intake or output. The receptors in your blood vessels signal the brain to change your breathing depth to meet the demands of the activity you are performing. Doing exercise increases the demand for air and your body responds naturally with a higher tidal volume. The volume taken in with each breath increases in attempt to take in more O2 and dispose of more CO2. Exercise causes an increase in tidal volume because your requirements for oxygen go up. An increase in tidal volume is necessary to effectively meet the oxygen requirements, as an increase in your rate of respiration alone is not sufficient.
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